A compound of formula (I) is a key intermediate for Dabigatran etexilate, which is known as an orally active prodrug for the reduction of stroke and systemic embolism. It was first disclosed in WO 98/37075. Processes for the manufacture of dabigatran etexilate are also known from WO 2006/000353 or described by Hauel et al. (J. Med. Chem, 2002, 45. 1757 ff).
Another process for the manufacture of Dabigatran is described by Zerban et al. (WO2006000353), However this process requires the use of an ecologically unfavorable dehydration agent.
Therefore a new process was developed by Gnad et al., as described in WO 2011/061080, circumventing the use of this dehydration agent. This process requires the use of the herein described intermediate 4-AMBA.
One of the current manufacturing routes of 4-aminobenzoamidine starts from 4-aminobenzonitrile via the 4-amino-N-hydroxybenzamidine intermediate (IV) (see Scheme 2).

This process requires usage of the expensive catalyst Pd/C and the hazardous reagent NH2OH, which is explosive and potentially mutagenic (Zerban Georg et al WO 2007/071743). It is well known that imidates can be prepared through the so called Pinner reaction by condensing a nitrile and an alcohol in the presence of anhydrous hydrogen chloride, hydrogen bromide or a base (Journal of Polymer Science, Part B: Polymer Physics (2011), 49, 649).
The prior art already describes a process for preparing Intermediate (II) (R=ethyl) Ethyl 4-aminobenzimidine and subsequent transformation to 4-AMBA (I) through Pinner reaction. However this process suffers from serious drawbacks for application on commercial scale. Thus described by Xiao-Hua Ma et al in Journal of Polymer Science, Part B: Polymer Physics (2011), 49, 649, the reaction was conducted at elevated temperatures on small scale and with reaction times of 20 h and bubbling of Hydrogen Chloride through the solution. On larger scale however, the high temperature and the long reaction time lead to uncontrollable decay of the reaction intermediates resulting in low yields and unsafe conduction of the reaction. Additionally the chosen setup is suitable for lab scale only and the used absolute ethanol renders the synthesis uneconomical. Use of cheaper alcohol solvents has not been described, most probably due to bad solubility of the intermediates in those solvents.
The problem underlying the present invention is to provide a process which circumvents the use of toxic, explosive or very expensive ingredients. Preferably the aim of the present invention is to overcome the drawbacks linked to the present process and to deliver an efficient, scalable, ecological feasible, robust and safe process for the manufacture of 4-AMBA (I) starting from 4-ABN (III), therefore requiring shorter reaction times, lower temperatures and circumventing the use of expensive reagents or solvents.